1. Field of the Invention
This invention relates to the dynamic sizing of bus transactions having multiple data sizes. In particular, the invention relates to dynamic sizing for 32-bit data bus and 64-bit/32-bit inter-operability in a 64-bit processor.
2. Description of Related Art
In a typical microprocessor architecture, the size of the data bus is directly related to the processor performance. Modern high performance microprocessors typically have a data bus size of 64-bit or above. The large data bus size increases the data transfer rate and provides fast processing in instruction and operand fetching. An example of a 64-bit processor is the PENTIUM.RTM. processor produced by Intel Corporation of Santa Clara, Calif.
To effectively utilize this large data bus, it is desirable that external components have a comparable data size. However, many devices are designed for smaller data sizes, such as 32-bit size. When these devices are interfaced to a 64-bit processor, additional data bus steering logic circuitry is necessary to perform the data switching to accommodate both 64-bit and 32-bit devices. This additional circuitry increases hardware and power consumption.
Furthermore, in applications requiring compactness and lower power consumption such as mobile computing and notebook computers, it is important to keep the form factor small by having a smaller data bus size without significantly sacrificing the system throughput. Reducing the external data bus size while still maintaining the internal bus size provides a solution for such applications.
In other applications, upgradability is important. In these applications, the system is initially designed for a smaller data size. As the application becomes more mature or customers demand higher throughput, the system is then upgraded to a larger size data configuration. It is costly to replace the interface circuitry for such an upgrade.
It is therefore desirable to have a method and apparatus for dynamic sizing of a bus transaction to provide flexibility and dual bus size inter-operability.